91 Octane: hard to find in US?

[Tom Reingold]

My only point was that it's generally less cost effective to spend (in
US dollars) $5 to boost 20 gallons of 91/92 octane than to buy
marginally more expensive 93/94 octane fuel if available. Some people
are even silly enough to use this stuff on regular unleaded when
mid-grade or premium are available.

And Hamburger Helper costs more (per pound) than hamburger meat! :-D

Tom

 

[JD]

This discussion is fascinating, thanks!

I should clarify that while 87-89-91 is the standard at most stations,
Sunoco sells four grades, going up to 94 I think. In fact 91 isn't
one of them, maybe it's 87-89.5-92-94? Not sure. Since it would
require driving up to the pump (recall that the stations here only
post 87 prices on the big sign), I've never compared 91 at
Petro-Canada to Sunoco's 92 (or whatever my Forester's minimum would
be) to see if there's a significant price differential. Now I'll have
to, I guess.

And there's another brand with a "Magnum" gas that's either 94 or 96,
I don't remember.

Yes. Sunoco's 94 octane uses ethanol as an additive to attain 94 octane.
Petrocan does it in Vancouver and Montreal but they use an oxygenating agent
so it contains more energy per liter.

 

[JD]

BTW - AKI is the same as (R+M)/2.

I am well aware of that. However, the original meaning of "octane" was the
percentage of octane blended with heptane to make the gasoline.
Consequently, you could not exceed 100 octane or 100% octane. The AKI (or
r+m)/2 is the resistance to detonation under compression and is an
equivalent to octane rating up to 100. Higher octane ratings resist
detonation even better than pure octane.

You made it sound like 93 octane fuel would have to be astronomically
expensive in Canadian. Perhaps marginally more, but not 2-3X times
the price like racing fuels. If oxygenates are needed to boost the
octane rating, ethanol is legal and used in Canada. 93 octane fuel
could also be made without oxygenates. If there's any reason why
you can find 93 octane in the NE US and not in Canada, it's more
likely than not a business decision. When the pumps in California's
major brand name gas stations went from 92 to 91, it was also a
marketing decision.

I'm guessing the "additive" you're referring to is MTBE, which was
supposed to have been phased out in California by 2002. The deadline
was extended to 2003. The spec sheets I saw for the 100 octane 76
racing gas says it contains MTBE. I don't know if any equivalent
product uses MTBE. Possibly not. I think the petroleum companies
liked using MTBE in fuel because it's a byproduct of refining.
Blending it in fuel was an easy way to get rid of it.

MTBE is one of the additives not legal in fuels in Canada, as is toluene
because of its toxicity and corrosive effects. Because of that, the options
for increasing octane are very few compared with what is allowed in the US.
Ethanol and methanol are options, but as yet increase the cost of fuel
significantly because alcohol doesn't mix well with gas so other agents have
to be added to make it blend properly. To my knowledge, only the Sunoco
refinery in Ontario yet does it.

The other options are oxygenation. Petrocan does that in selected markets
where the cost is subsidized. Even then, 94 octane Petrocan is nearly 8
cents per liter more than 91; which is 16 cents per litre more than 87.
That is nearly 50/gal in US dollars which would make it difficult to sell
except to those people who are willing to pay for performance fuels. Hell,
we have seen people wanting to use 87 or 89 in their WRXs on this board.

 

[JD]

93 octane "super premium" is recommended for the WRX STi.

Yes, and it says 91 minimum. I have my owner's manual in front of me.

 

[JD]

This isn't true. My old 80s boat car, in the final years before I bought
my
STi, wouldn't run smoothly on anything but 94 octane. It was old, crappy,
had serious problems: and 94 octane made it run nicer, with less knocking.


Recommended by who? Your implication by ommission is that higher octane is
*not* recommended by car manufacturers. I'd love to hear which ones state
that "only octane of this value is recommended. Higher octane is not."


This is the part where you explain how the higher octane is somehow bad
for
your car.

Probably because of carbon deposits. That can happen in older cars and it
causes an increase in compression. When that happens, you'll get knocking
on lower octane fuels. If the car is working well, higher octane does
nothing for it.

 

[y_p_w]

Probably because of carbon deposits. That can happen in older cars and it
causes an increase in compression. When that happens, you'll get knocking
on lower octane fuels. If the car is working well, higher octane does
nothing for it.

Your assumption about higher octane fuel leading to more carbon
deposits is incorrect with modern fuels. There was a time when higher
octane fuels typically contained higher levels of olefins. The olefins
also led to increased gum/varnish as well as engine deposits from
incomplete burning. Modern reformulated fuel in all grades is far
lower in olefins. Even back then, several higher octane fuel brands
would use higher levels of detergents to compensate.

<http://www.chevron.com/products/prodserv/fuels/bulletin/motorgas/3_refining-testing/default.asp>

"With the advent of air pollution regulations, property specifications
have been supplemented by some composition specifications. As noted in
Chapter 2, the first gasoline-related air pollution regulation limited
the amount of olefins in gasoline sold in Southern California by
establishing a Bromine Number maximum specification. More recent
regulations limit the amounts of both olefins and aromatics in
reformulated gasolines."

BTW - apparently it's illegal for refiners to add manganese to
gasoline in California, which would include MMT.

 

[JD]

Your assumption about higher octane fuel leading to more carbon
deposits is incorrect with modern fuels. There was a time when higher
octane fuels typically contained higher levels of olefins. The olefins
also led to increased gum/varnish as well as engine deposits from
incomplete burning. Modern reformulated fuel in all grades is far
lower in olefins. Even back then, several higher octane fuel brands
would use higher levels of detergents to compensate.

I didn't say that. I said that as an engine gets older (particularly if it
is on the highway frequently after being used for city driving) it can build
up hard carbon deposits. Doesn't matter what kind of fuel. Whne that
happens, it increases compression in the cyclinder and higher octane fuel
will reduce that. Hence, older cars frequently work better on higher octane
fuel even if they were designed for regular.

 

[y_p_w]

I didn't say that. I said that as an engine gets older (particularly
if it is on the highway frequently after being used for city driving)
it can build up hard carbon deposits. Doesn't matter what kind of
fuel. Whne that happens, it increases compression in the cyclinder
and higher octane fuel will reduce that. Hence, older cars frequently
work better on higher octane fuel even if they were designed for
regular.

Sure - higher octane fuel is a crutch for other problems such as heavy
carbon deposits. However - the quality of the deposit control
additives in current fuels is extremely high and the composition has
changed with reformulated fuel. Carbon deposits shouldn't be the
problem they were 15 years ago. And even if they do happen, some of
the aggressive detergent treatments (Techron Concentrate, BG 44K,
Regane) are known to work wonders.

Sorry - I had a little confusion - the original comment about turning
down 91 octane was from "Moon Guy". My comment was really directed
at him. There is no reason why he shouldn't have used it at the same
price as regular given the composition of modern reformulated gasolines.

 

[k. ote]

y_p_w wrote:

My only point was that it's generally less cost effective to spend (in
US dollars) $5 to boost 20 gallons of 91/92 octane than to buy
marginally more expensive 93/94 octane fuel if available. Some people
are even silly enough to use this stuff on regular unleaded when
mid-grade or premium are available.

Definite agreement.

On a sad note, I'm noticing some engine ping recently, and I'm using 94
octane up here in Canada. Sucks to be me.

 

[y_p_w]

I didn't say that. I said that as an engine gets older (particularly
if it is on the highway frequently after being used for city driving)
it can build up hard carbon deposits. Doesn't matter what kind of fuel.
Whne that happens, it increases compression in the cyclinder and higher
octane fuel will reduce that. Hence, older cars frequently work better
on higher octane fuel even if they were designed for regular.

Detonation is supposed to be from a curve of pressure and/or
temperature. Hard carbon deposits might result in a slightly higher
compression as they displace some of the combustion chamber volume.
That contribution to compression ratio increase is supposed to be
minor compared to the residual heat that is trapped by the carbon,
especially if the carbon is on the valves.

<http://www.germanmotorcars.com/Detonation.htm>

 

[JD]

Sure - higher octane fuel is a crutch for other problems such as heavy
carbon deposits. However - the quality of the deposit control
additives in current fuels is extremely high and the composition has
changed with reformulated fuel. Carbon deposits shouldn't be the
problem they were 15 years ago. And even if they do happen, some of
the aggressive detergent treatments (Techron Concentrate, BG 44K,
Regane) are known to work wonders.

Sorry - I had a little confusion - the original comment about turning
down 91 octane was from "Moon Guy". My comment was really directed
at him. There is no reason why he shouldn't have used it at the same
price as regular given the composition of modern reformulated gasolines.

Agreed. I wouldn't spend the extra money since it won't make a car work
better unless it needs it for some reason, but it won't hurt either. So, at
the same price, I would take it too.

 

[JD]

Detonation is supposed to be from a curve of pressure and/or
temperature. Hard carbon deposits might result in a slightly higher
compression as they displace some of the combustion chamber volume.
That contribution to compression ratio increase is supposed to be
minor compared to the residual heat that is trapped by the carbon,
especially if the carbon is on the valves.

<http://www.germanmotorcars.com/Detonation.htm>

We once tested a "high compression" engine that had a designed compression
ratio of 11.5:1 and the head pressure at TDC was supposed to be about 186
PSI at sea level. The head pressure was actually about 210 PSI and that
worked out to almost 13:1; too high for regular gas. The car was 15 years
old and had been an old person's car. It was bought by a kid and it was
driven hard. That is pretty significant. However, the car worked better on
89 (only pinged on hard acceleration) and worked fine on 91.

 

[JD]

y_p_w wrote:



Definite agreement.

On a sad note, I'm noticing some engine ping recently, and I'm using 94
octane up here in Canada. Sucks to be me.

What kind of car? That sounds like an STi problem. I had it. Seemed to be
most prominant when it was hot out. The dealer did a reflash of the ECU and
the problem went away.

 

[y_p_w]

We once tested a "high compression" engine that had a designed compression
ratio of 11.5:1 and the head pressure at TDC was supposed to be about 186
PSI at sea level. The head pressure was actually about 210 PSI and that
worked out to almost 13:1; too high for regular gas. The car was 15 years
old and had been an old person's car. It was bought by a kid and it was
driven hard. That is pretty significant. However, the car worked better on
89 (only pinged on hard acceleration) and worked fine on 91.

Sounds like "grandpa" didn't run the car hard enough to hear any knock.

However - I'm just trying to point out that the residual heat from
moderate carbon deposits will affect the octane requirement before
increased compression from heavy carbon deposits will. The case
you cite seems to be rather extreme.

 

[k. ote]

What kind of car? That sounds like an STi problem. I had it. Seemed to
be
most prominant when it was hot out. The dealer did a reflash of the ECU
and the problem went away.

Yes, Canadian-spec STi, 2004 model. According to a few forums on NASIOC,
there was a wide-spread annoyance with engine ping, and Subaru came out
with a quick-fix ECU flash within.. what was it? A few days?

How long did it take them to reflash your ECU? There're reports of there
being only a single reflashing unit in all the U.S. (or there was, for a
while) so peoples' cars were being held for up to a week while the
operation continued.

Did you notice any difference in power or response before and after?

 

[JD]

Yes, Canadian-spec STi, 2004 model. According to a few forums on NASIOC,
there was a wide-spread annoyance with engine ping, and Subaru came out
with a quick-fix ECU flash within.. what was it? A few days?

How long did it take them to reflash your ECU? There're reports of there
being only a single reflashing unit in all the U.S. (or there was, for a
while) so peoples' cars were being held for up to a week while the
operation continued.

Did you notice any difference in power or response before and after?

They did it as part of scheduled maintenance and no hold-up at all. I
noticed it being a bit less zippy at the bottom end, and the power came on
more quickly near the top. However, when in the meat of power band, I
didn't really notice much difference at all; except that there was much less
pinging. It still pings a bit when it is really hot out, or if I have been
sitting in traffic and the intercooler is hot. However, a shot of spray and
it goes away.

 

[JD]

Sounds like "grandpa" didn't run the car hard enough to hear any knock.

However - I'm just trying to point out that the residual heat from
moderate carbon deposits will affect the octane requirement before
increased compression from heavy carbon deposits will. The case
you cite seems to be rather extreme.

Whatever. The point is that older engines, even when designed for regular,
will frequently work much better on higher octane than on regular whatever
the reasons for it because the higher octane resists combustion before the
ignition.

 

[Jimmy Joe]

My Forester XT wants 91 octane, which is not difficult here in Canada
where most stations sell 87, 89, and 91. Sunoco's the exception I
know of with something weird for its four grades.

I was in the US last month and most stations were 87, 89, and 93. So
I put in 93. Was that the right decision? Sunoco had 87, 89, 91 and
93 (I think) so I used 91. It was only 2c/gal cheaper than 93, so if
there wasn't a convenient Sunoco I just used 93 from someone else.

How come 91 is so hard to find? And what do American XT owners do,
put in 93? Should I look for something higher than 91 myself when I'm
at home?

Thanks!
=aw


andrew [(e-mail address removed)]

You can find 91 all over the place in the US. East coast you get
luckier with 93 and 94 found at the pumps

 

[k. ote]

91 or 93 makes no difference to the engine, only your billfold

Yea.. right. Another non-performance car driver who thinks that because
there's no difference in his car, there's no difference in anyone's car.